OPPONENTS of a massive gold, copper and molybdenum mining operation proposed for the headwaters of Alaska’s salmon-rich Bristol Bay are not letting their guard down.

The announcement earlier this month that London-based Anglo American would end its partnership with Canada’s Northern Dynasty Minerals to develop the Pebble mine was well-received by critics, but no one assumes the fight is over.

Everything about the Pebble mine is huge — the potential mineral recovery, the scale of the project and the potential for disaster in one of the world’s most vibrant fisheries.

Anglo American’s departure is no small matter. The company had reportedly invested a half-billion dollars since the partnership began in 2007.

Still, in July, U.S. Sen. Lisa Murkowski of Alaska, asked the partnership to present a specific plan for what was proposed.

At the same time the proponents were touting economic benefits, they were too vague about the details for the Republican senator and others.

The U.S. Environmental Protection Agency is using its authority under the Clean Water Act to review, and the agency has not been impressed.

The project is enormous. Mining waste would be held behind three dams or embankments up to 740 feet high, with one of them estimated to be 4.5 miles long. The three dams would total 9 miles in length.

This all would be in a setting of enormous economic impact for the state. Last year Alaska’s fishing industry caught 22 million salmon in Bristol Bay. The bounty of salmon also powers substantial sport-fishing and tourism business.

Pebble mine is a hazard to where Bristol Bay salmon spawn and a fishing economy in Washington and Oregon.

The mine is a bad idea, but a financial setback for the proposal does not mean the threat has gone away.